The present invention relates to a tire parameter deriving method for deriving a tire dynamic element parameter indicating a cornering characteristic of the tire based on a tire dynamic model constituted by using a plurality of tire dynamic element parameters, a tire cornering characteristic calculating method for calculating the cornering characteristic of a tire based on the tire dynamic model, and a tire designing method for designing a tire and a vehicle dynamics analyzing method using the above method, and also to a program for allowing a computer to execute the tire parameter deriving method.
Various methods for evaluating and analyzing vehicle dynamic characteristics by using a computer are currently utilized. For the analysis of the dynamic characteristics, information of a cornering characteristic of a tire provided between a vehicle body and a road surface is required. The cornering characteristic of the tire is generally defined by using a tire model. As the tire model, a non-analytic model such as a “Magic Formula” has recently been proposed.
The “Magic Formula” is a non-analytic model describing tire characteristics by determining factors B to E in the following Formula (1) so that measured data of a lateral force and measured data of a self-aligning torque are approximated in an excellent manner by a function expressed by the Formula (1).Y(x)=D·sin [C·tan−1{B·x−E·(B·x−tan−1(B·x))}]  (1)
The “Magic Formula” expressed by the above Formula (1) can be effectively used as a cornering characteristic of a tire so as to evaluate and analyze dynamic characteristics of a vehicle. However, the “Magic Formula” is a model obtained by exclusively describing a cornering characteristic of a tire as a tire characteristic, neglecting an actual dynamic behavior of the tire. Therefore, the above-mentioned factors B to E do not represent any dynamic mechanism affecting the cornering characteristic of a tire. Therefore, even if the factors B to E are successfully obtained, these factors have no relation and correlation with tire dynamic element parameters such as various stiffnesses affecting the cornering characteristic of the tire. Therefore, there is conventionally a problem that a tire cannot be designed based on various stiffnesses of the tire via the above-mentioned tire model.
On the other hand, as a tire dynamic model representing the cornering characteristic of a tire using the tire dynamic element parameters such as various stiffnesses of the tire, a tire dynamic model obtained by modifying a Fiala model described in a non-patent document of “Study of a Semi-Empirical Tire Model for Vehicle Dynamics Analysis—Part 1 Under the Condition of Constant Velocity—” by Kazuo Araki, Hideo Sakai and Minao Yanase, Transactions of Society of Automotive Engineers of Japan, Vol. 24 (2), 59 (1993) is known.
However, the “tire model” described in the above document has the following problem. Even if tire dynamic element parameters can be calculated so that calculated data of a lateral force is identical with its measured data, calculated data of a self-aligning torque generated with the lateral force cannot be identical with its measured data. In particular, if a slip angle is equal to or larger than 5 degrees, the calculated data greatly differs from the measured data.